The present invention relates to a belt-type continuously variable transmission and more specifically to a step motor positioning structure for positioning a step motor that drives a speed-change control valve for controlling an oil pressure to be supplied to a pulley of a belt-type continuously variable transmission.
It is known that a belt-type continuously variable transmission using a V-belt (hereinafter referred to simply as belt-type CVT) is suited for use in vehicles.
Referring to FIG. 8, an example of a belt-type CVT will be described.
The belt-type CVT includes a speed-change mechanism 100 whose principal portion is constituted by a pair of pulleys, i.e., a primary pulley 16 on the input shaft 15 side and a secondary pulley 26 on the output shaft 30 side. The input shaft 15 is connected to an engine by way of a forward and reverse switching mechanism 14 and a torque converter (not shown) having a lock-up clutch.
The pulleys 16, 26 of the speed-change mechanism 100 are drivingly connected to each other by a V-belt 12.
The primary pulley 16 consists of a fixed sheave 16a rotatable together with the input shaft 15 and a movable sheave 16b axially movable relative to the fixed sheave 16a so as to form therebetween a pulley groove of a variable width. The secondary pulley 26 consists of a fixed sheave 26a rotatable together with the output shaft 30 and a movable sheave 26b axially movable relative to the fixed sheave 26a so as to form therebetween a pulley groove of a variable width.
The primary pulley 16 and secondary pulley 26 are provided with a primary cylinder chamber 17 and a secondary cylinder chamber 27 and supplied with a primary pressure and secondary pressure from an oil pressure control section 105, respectively.
The oil pressure control section 105 generates a line pressure by regulating an oil pressure from an oil pump OP. Further, the oil pressure control section 105 controls the line pressure in response to a command from a CVT control unit 103 to produce a primary pressure and a secondary pressure.
During running of a vehicle, the widths of the pulley grooves of the primary pulley 16 and secondary pulley 26 are varied depending upon a variation of an oil pressure supplied to the respective cylinder chambers 17, 27, thus varying the winding diameters of the belt 12 wound around the pulleys 16, 26 thereby varying the transmission ratio between the primary pulley 16 and the secondary pulley 26 continuously.
FIG. 9 shows a primary pressure supply circuit structure in the oil pressure control section 105 for supplying a primary pressure to the primary pulley cylinder chamber 17. The oil pressure control section 105 (refer to FIG. 8) includes a speed-change control valve 35 for controlling the primary pressure through control of the line pressure. Herein, the line pressure serves as the second pressure and is supplied to the secondary cylinder chamber 27.
The speed-change control valve 35 has a valve spool 36 connected to an intermediate portion of a servo link 50 that constitutes a mechanical feedback device and is driven by a step motor 40 connected to an end of the servo link 50. The other end of the servo link 50 is connected to a pulley follower 45 that follows movement of the movable sheave 16b of the primary pulley 16. By this, the shift control valve 35 receives feedback of the width of the pulley groove of the primary pulley 16, i.e., the actual transmission ratio.
The transmission ratio between the primary pulley 16 and the secondary pulley 26 is controlled by the step motor 40 that operates in response to a speed-change command signal from the CVT control unit 103.
In the meantime, the line pressure is controlled to a predetermined value in accordance with an engine operating condition, by means of a pressure control valve (not shown) and based on a command (e.g., a duty signal) from the CVT control unit 103.
FIGS. 10 and 11 show a step motor attaching structure according to an earlier technology.
Right under the primary pulley 16 and within a transmission case 102 is disposed a guide shaft 108 that is positioned between the transmission case 102 and a pulley support block 106 and in parallel with an axis of rotation of the primary pulley 16. The pulley support block 106 is fixedly disposed within the transmission case 102. The pulley follower 45 is slidably supported on the guide shaft 108.
The pulley follower 45 has a sleeve portion 46 rotatable on the guide shaft 108 and an engagement portion 47 extending from the sleeve portion 46 toward the primary pulley 16 side.
The engagement portion 47, when viewed in the axial direction of the guide shaft 108, is in the form of a circular arc corresponding to the outer periphery of the movable sheave 16b of the primary pulley 16. The engagement portion 47 has a first surface 47A in contact with the movable sheave 16b, which first surface is located on the side opposite to the fixed sheave 16a side and a second surface 47B in contact with the outer circumferential periphery of the movable sheave 16b. 
The pulley follower 45 is always urged against the movable sheave 16b (refer to FIG. 8) by means of a spring 58 disposed between the transmission case 102 and the pulley follower 45 and slidably movable on the guide shaft 108 in accordance with a variation of the axial position of the movable sheave 16b. 
The sleeve portion 46 of the pulley follower 45 is provided with a pin support portion 49. Under the condition where the engagement portion 47 is in contact with the peripheral portion of the movable sheave 16b, the pin support portion 49 protrudes vertically upward from the sleeve portion 46 while allowing a connecting pin 48 to extend horizontally.
The speed-change control valve 35 includes a valve bore (refer to FIG. 9) in parallel with the guide shaft 108 and a valve spool 36 slidably disposed in the valve bore.
The step motor 40 is disposed adjacent the speed-change control valve 35 and on the side thereof opposite to the guide shaft 108. An output rod 42 of the step motor 40 extends in parallel with the guide shaft 108.
The step motor 40 is attached to a stationary support (not shown) as follows. First, a motor bracket 41B integral with the step motor 40 is placed on the stationary support. Then, two bolts 63 are screwed into corresponding threaded holes of the stationary support through respective bolt holes of the motor bracket 41B and tightened to fix the motor bracket 41B to the stationary support.
The output rod 42 of the step motor 40 has a bifurcated end portion and is provided with a pin 43 at the bifurcated end portion. The valve spool 36 of the speed-change control valve 35 has at an end thereof a block 37 which is formed with a pivot pin hole (no numeral).
The servo link 50 extends vertically and has an intermediate portion to which a pivot pin 55 is fixedly attached. The pivot pin 55 is rotatably fitted in the pivot pin hole of the block 37 of the valve spool 36.
The servo link 50 is in the form of a plate and has a straight line shape. The servo link 50 has axially opposite bifurcated end portions 52, 53, one 52 of which is engaged with the connecting pin 48 of the pulley follower 45 by holding the pin 48 between the prongs thereof and the other 53 of which is engaged with the connecting pin 43 of the output rod 42 of the step motor 40 by holding the pin 43 between the prongs thereof. Namely, the servo link 50 is swingably or pivotally connected at the opposite ends to the pulley follower 45 and the output rod of the step motor 40 and at the intermediate portion to the valve spool 36 of the speed-change control valve 35.
In accordance with movement of the servo link 50 that is responsive to an operation of the step motor 40, the valve spool 36 is axially moved to cause the speed-change control valve 35 to perform supply or discharge of oil pressure to or from the primary cylinder chamber 17 and thereby control the primary pressure so that a target transmission ratio commanded by the driving position of the step motor 40 is attained. After the movable sheave 16b is moved to complete a speed-change, the speed-change control valve 35 is closed in response to pivotal movement of the servo link 50 in the opposite direction.